Liquid-cooled electrical machine with parallel flow

ABSTRACT

An electrical machine comprising a rotor ( 26 ) mounted on a shaft ( 29 ) for rotation therewith and defining an axis of rotation, and a stator ( 54 ) disposed coaxially with and in opposition to the rotor ( 26 ). The electrical machine further comprises a housing ( 22, 24 ) enclosing the stator ( 54 ) and the rotor ( 26 ), the housing ( 22, 24 ) having a first axial end with a wall with an inner surface and an outer surface and a second axial end with a wall with an inner surface and an outer surface. The electrical machine also includes a first cooling tube ( 80 ′) having a first end and a second end and an embedded portion thereof embedded between the first inner surface and the first outer surface of end wall ( 81 ). A second cooling tube ( 82 ′) has a first end and a second end and an embedded portion thereof embedded between said inner surface and said outer surface of the wall ( 83 ) of the second axial end. The first end ( 226 ) of the first cooling tube and the first end ( 228 ) of the second cooling tube ( 82 ′) are fluidically coupled together to permit fluid flow in parallel between the first cooling tube ( 80 ′) and the second cooling tube ( 82 ′).

RELATED APPLICATIONS

The present invention is also related to U.S. patent application Ser.No. 09/634,411 entitled “Liquid-Cooled Electrical Machine With IntegralBypass” incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to electrical machines, and moreparticularly to cooling of electrical machines.

DESCRIPTION OF THE RELATED ART

Ways are continually sought to increase the electrical output ofautomotive alternators. With increased electrical output comesadditional heat generated in the various electrical components of thealternator. In addition, friction in the bearings which support therotor shaft of the alternator also generates heat. Because heatgenerated in an alternator is frequently the factor which limits theelectrical output of the alternator, effective cooling of the alternatoris very important.

Circulating liquid within an alternator has been recognized as one meansfor providing cooling. A liquid cooling design which provides effectivecooling and which can support demands for ever-reducing package size ofthe alternator can be particularly advantageous.

SUMMARY OF THE INVENTION

The present invention provides an electrical machine comprising a rotormounted on a shaft for rotation therewith and defining an axis ofrotation, and a stator disposed coaxially with and in opposition to therotor. The electrical machine further comprises a housing enclosing thestator and the rotor, the housing having a first axial end with a wallwith an inner surface and an outer surface and a second axial end with awall with an inner surface and an outer surface. The electrical machinealso includes a first cooling tube having a first end and a second endand an embedded portion thereof embedded between the first inner surfaceand the first outer surface. A second cooling tube having a first endand a second end and an embedded portion thereof embedded between saidinner surface and said outer surface of the wall of the second axialend. The first end of the first cooling tube and the first end of thesecond cooling tube are fluidically coupled together to permit fluidflow in parallel between the first cooling tube and the second coolingtube.

Designs according to the present invention are advantageous in that theycan provide effective cooling of an electrical machine while alsosupporting packaging-efficient electrical machine designs.

Other objects and features of the present invention will become apparentwhen viewed in light of the detailed description of the preferredembodiment when taken in conjunction with the attached drawings andappended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an alternator 20 according to oneembodiment of the present invention.

FIG. 2 is a cross-sectional view of alternator 20 taken along a planeparallel to the axis of rotation of alternator 20.

FIG. 3 is a perspective view of rotor 26 of alternator 20.

FIG. 4 is a cross-sectional view of alternator 20 taken along line 4—4of FIG. 2.

FIG. 5 is a cross-sectional view of alternator 20 taken along line 5—5of FIG. 2.

FIG. 6 is a perspective view of a second embodiment of the invention.

FIG. 7 is a rotated perspective view of the second embodiment shown inFIG. 6.

FIG. 8 is a partially exploded view of the second embodiment shown inFIG. 6.

FIG. 9 is a perspective of one housing portion having an inlet accordingto the present invention.

FIG. 10 is a partially cutaway perspective view of a portion of thehousing of FIG. 10.

FIG. 11 is a perspective view of second embodiment of an inlet accordingto the present invention.

FIG. 12 is a partial cross-sectional view through the inlet of FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Refer first to FIGS. 1-3, an alternator 20 includes a front housingportion 22 and a rear housing portion 24 which are suitably bolted orotherwise attached together. Front housing portion 22 and rear housingportion 24 are preferably metallic. Included within front housingportion 22 and rear housing portion 24 is a rotor 26. Those skilled inthe art will recognize rotor 26 as being generally of the “claw-pole”variety. A plurality of permanent magnets 28 are disposed within rotor26 in order to enhance the electrical output of alternator 20.

Rotor 26 includes a shaft 29 having two slip rings 30 and 32 which aremeans for providing electrical power from a voltage regulator (not shownin the particular sectioning employed in FIG. 2) to a field coil 34disposed within rotor 26. Also coupled to shaft 29 is a pulley 36, orother means for rotating rotor 26. Shaft 29 is rotatably supported by afront bearing 50, itself supported by front housing portion 22, and arear bearing 52, rotatably supported by rear housing portion 24.

A stator 54 is disposed in opposition to rotor 26. Stator 54 includes aferromagnetic stator core 56, on which stator windings 58 are wound. Theend turns 60 of stator windings 58 on one axial side of stator core 56are substantially enclosed in a groove 62 in front housing 22. The endturns 64 of stator winding 58 on the other axial side of stator core 56are substantially enclosed in a groove 66 in rear housing 24.Preferably, end turns 60 and 64 are encapsulated in a highly thermallyconductive compound in order to facilitate heat transfer away fromstator windings 58.

A rectifier 70, coupled to stator windings 58 in order to rectify thealternating current output generated in stator windings 58 by theoperation of alternator 20, is mounted to rear housing 24. Rectifier 70includes a negative rectifier plate 72, which forms the commonconnection for the cathodes of the “negative” diodes 72A. Rectifier 70also includes a positive rectifier plate 74, which forms the commonconnection for the anodes of the “positive” diodes 74A. Negativerectifier plate 72 and positive rectifier plate 74 are electricallyinsulated from one another. A plastic cover 76 covers the rear ofalternator 20, including rectifier 70. Electrical connectors 77 and 78provide the required electrical connections to and from alternator 20.As those connections are conventional, they are not described in detailhere.

Front housing portion 22 also includes cooling tube 80, and rear housingportion 24 includes cooling tube 82. Cooling tubes 80 and 82 arepreferably metallic, in order to assure good heat transfer from housingportions 22 and 24 to cooling tubes 80 and 82, respectively. Coolingtubes 80 and 82 are preferably die-cast into their respective axial endwalls 81, 83 of housing portions 22 and 24. Of course, if cooling tubes80 and 82 are included within housing portions 22 and 24 by die casting,the material comprising cooling tubes 80 and 82 must have a highermelting temperature than the material comprising housing portions 22 and24, in order to allow cooling tubes 80 and 82 to be die-cast therein.

The ends of cooling tube 80 emerge from front housing portion 22, andthe ends of cooling tube 82 emerge from rear housing 24. End 84 ofcooling tube 80 forms an inlet into which cooling fluid can beintroduced into alternator 20. End 86 of cooling tube 82 forms an outletfrom which cooling fluid exits from alternator 20. The remaining twoends of cooling tube 80 and cooling tube 82 are coupled together by a“cross-over” formed by flexible tube 88 and two clamps 90 and 92.Cooling fluid can thus flow into inlet end 84 of cooling tube 80,through the length of cooling tube 80, through the “cross-over” intocooling tube 82, through the length of cooling tube 82, and out theoutlet end 86 of cooling tube 82. Inlet end 84 and outlet end 86 arecoupled to a source of cooling fluid such as the cooling system of amotor vehicle engine.

Referring now to FIG. 4, it can be seen that cooling tube 80 is formedsubstantially as a circular loop until points 100 and 102, where coolingtube 80 begins to emerge from front housing portion 22.

Referring now additionally to FIG. 5, it can be seen that cooling tube82 is also formed in a substantially circular loop until points 104 and106, where cooling tube 82 begins to emerge from rear housing portion22.

The design disclosed herein is particularly effective for coolingalternator 20, for a number of reasons. First, end turns 60 and 64 ofstator 54 are substantially enclosed by grooves 62 and 66 in the housingof alternator 20. Because the housing is cooled by cooling tubes 80 and82, heat generated in stator windings 58 is effectively conducted awayfrom those windings. Second, front housing portion 22 presents a large,substantially flat surface 108 to rotor 26 across a small air gap 110.Air gap 110 is preferably about 0.5 millimeters wide. Because fronthousing portion 22 is cooled by cooling tube 80, the large, flat surface108 across small air gap 110 provides for substantial heat transfer awayfrom rotor 26, including heat generated in field coil 34. Rear housingportion 24 presents a similar large, substantially flat surface 112 torotor 26 across a small air gap 114. Air gap 114 is preferably about 0.5millimeters wide. Third, with bearings 50 and 52 mounted in housingportions 22 and 24 and in proximity with cooling tubes 80 and 82, heatgenerated in bearings 50 and 52 due to rotation of shaft 29 iseffectively conducted away.

The design disclosed herein provides the cooling advantages describedimmediately above, while also contributing to alternator 20 having ashort axial length. It can be seen that the axial alignment of coolingtube 80, end turns 60 and bearing 50, as well as the axial alignment ofcooling tube 82, end turns 64 and bearing 52 cause alternator 20 to havethe short axial length. This is very much an advantage in packagingalternator 20 in a vehicle.

Referring now to FIGS. 6 and 7, a second embodiment having parallel flowas opposed to the serial flow described above is illustrated. In thefollowing description the same reference numerals that are used above inthe first embodiment are primed for the same components in FIG. 6. Inthis embodiment, a fluid interface 220 is used for coupling fluids toalternator 20′. When fluid enters alternator 20′ through fluid interface220, fluid travels through cooling tube 80′ and cooling tube 82′simultaneously. The fluid then exits fluid interface 220 from bothcooling tube 80′ and cooling tube 82′. Fluid interface 220 has an inlet222 and an outlet 224. In the preferred embodiment, inlet 222 and outlet224 are coupled to the cooling system of an automotive vehicle. As willbe further described below, it is preferred to have a minimal pressuredrop across the alternator. Therefore, providing a parallel flow as inFIGS. 6 and 7 versus a series flow reduces the pressure drop by as muchas 70 percent. In the preferred embodiment, inlet 222 and outlet 224 arelocated on the same housing 22′. However, those skilled in the art wouldrecognize that inlet 222 and outlet 224 may also be located on housing24′.

To achieve the parallel flow the cooling tube 80′ has a first end 226fluidically and mechanically coupled to first end 228 of second coolingtube 82′. First end 226 and first end 228 are fluidically coupled toinlet 222. Second end 230 of first cooling tube 80′ is fluidically andmechanically coupled to second end 232 of second cooling tube 82′.Second end 230 and second end 232 are fluidically coupled to outlet 224.

An inlet hose interface 234 may be coupled to inlet 222. An outlet hoseinterface 236 is preferably coupled to outlet 224. Both inlet hoseinterface 234 and outlet hose interface 236 are mechanically coupled tothe respective inlet 222 and outlet 224. The mechanical coupling may befixed or may be rotatable to provide convenient assembly. Also, bylocating the inlet 222 and the outlet 224 on the same housing, the easeof assembly during manufacture of the vehicle is increased in the evershrinking underhood environment.

Referring now to FIG. 8, a partial exploded view of alternator 20′ isillustrated. As can be seen, fluid interface 220 has a first flange 238coupled adjacent to first end 226 and second end 230. A second flange240 is positioned adjacent first end 228 and second end 232 of secondcooling tube 82′. As is illustrated, each flange 238, 240 has nearly a“figure 8” shape. At least one of the flanges 238 and 240 preferablyhave a seal channel 242 formed therein. Seal channel 242 is sized toreceive a seal 244 at least partially therein. Seal 244 provides a sealbetween first flange 238 and second flange 240 to prevent fluid leakagetherebetween. These skilled in the art will recognize various types ofseals and gaskets may be used.

To conserve material a common wall 246 is preferably located betweenfirst end 226 and second end 230 of first cooling tube 80′.

Referring now to FIGS. 9 and 10, a third embodiment of the presentinvention is illustrated. In this embodiment the same reference numeralsused in the second embodiment will be used for the same components. Inthis embodiment, the common wall 246 between inlet 222 and outlet 224has a port 248 formed therethrough. Port 248 is sized to allow fluid topass directly through common wall 246 from inlet 222 and outlet 224. Byallowing fluid to pass directly between inlet 222 and outlet 224, thefluid resistance of the alternator is reduced. Moreoever, the amount offluid traveling through first cooling tube 80′ and second cooling tube82′ is sufficient to cool the alternator. Thus, because the pressuredrop across the alternator is reduced, a bypass manifold with itsassociated hoses and connection is not required.

Preferably, inlet 222, outlet 224 and port 248 are colinear along line250. However, those skilled in the art will recognize that anon-colinear alignment may be used with the risk of increasing thepressure drop across the alternator.

The diameter D of port 248 may be varied to increase or decrease thepressure drop across the alternator. The amount of pressure increase ordecrease across the alternator will vary depending on the particularvehicle configuration and cooling system flow requirements.

Referring now to FIGS. 11 and 12, a second embodiment of an alternativefluid interface 220′ is illustrated. Fluid interface 220′ in thisembodiment includes an inlet T-shaped portion 260 and an outlet T-shapedportion 262. Inlet T-shaped portion 260 is coupled to first end 226′ offirst cooling tube 80″ and first end 228′ of second cooling tube 82″.Outlet T-shaped portion 262 is coupled to second end 230′ of firstcooling tube 80″ and second end 232′ of second cooling tube 82″.Preferably, a flange 264 extends between first end 226′ and second end230′ of first cooling tube 80″. A second flange 266 preferably extendsbetween first end 228′ and second end 232′ of second cooling tube 82″.

As is best illustrated in FIG. 12, first cooling tube 80″ has areceiving portion 268 that extends into inlet T 260 that inlet T-shapedportion 260 may be received thereon. Also, second cooling tube 82″ has areceiving portion 270 extending therefrom. Receiving portion 270 alsoextends inward into inlet T 260 so that inlet T is receiving thereon. Aplurality of fields 272 such as O-rings are positioned between inletT-shaped portion 260 and receiving portions 268, 270. Seals 272 preventfluid leakage between the T-shaped portion 260 out of the fluid path.

Although FIG. 12 only illustrates a cross-sectional view through firstT-shaped portion 260, second T-shaped portion 262 is also configured ina similar manner.

Inlet T-shaped portion 260 has an inlet end 261 for receiving fluid fromthe coolant path of the automotive vehicle. Outlet T-shaped portion 262has an outlet end 263 for returning coolant to the coolant path of theautomotive vehicle. In this embodiment similar to the prior embodiment,coolant enters inlet end 261 and travels through first coolant tube 80″and second coolant tube 82″ in parallel so that coolant circulatestherethrough and exits simultaneously through outlet end 263.

Other embodiments may be formed as would be evident to those skilled inthe art. For example, the inlet 222 and outlet 224 may be located onalternate housing portions. Further, port 248 may be located in adifferent housing portion than inlet 222 and outlet 224.

Various other modifications and variations will no doubt occur to thoseskilled in the arts to which this invention pertains. Such variationswhich generally rely on the teachings through which this disclosure hasadvanced the art are properly considered within the scope of thisinvention. This disclosure should thus be considered illustrative, notlimiting; the scope of the invention is instead defined by the followingclaims.

What is claimed is:
 1. An electrical machine comprising: a rotor mountedon a shaft for rotation therewith and defining an axis of rotation; astator disposed coaxially with and in opposition to said rotor; ahousing enclosing said stator and said rotor; said housing having afirst axial end, said first axial end having a wall with a first innersurface and a first outer surface, said housing having a second axialend having a wall with a first inner surface and a first outer surface;a first cooling tube having a first end and a second end and an embeddedportion thereof embedded between said first inner surface and said firstouter surface of said wall of said first axial end; and, a secondcooling tube having a first end and a second end and an embedded portionthereof embedded between said first inner surface and said first outersurface of said wall of said second axial end; wherein said first end ofsaid first cooling tube and said first end of said second cooling tubeare fluidically coupled together to permit fluid flow in parallelbetween said first cooling tube and said second cooling tube.
 2. Anelectrical machine as recited in claim 1 wherein second end of saidfirst cooling tube and said second end of said second tube are coupledtogether.
 3. An electrical machine as recited in claim 1 furthercomprising a T-shaped portion having a fluid inlet fluidically coupledto said first end of said first cooling tube and said first end of saidsecond cooling tube.
 4. An electrical machine as recited in claim 1further comprising a T-shaped portion having a fluid outlet fluidicallycoupled to said second end of said second cooling tube and said secondend of said first cooling tube.
 5. An electrical machine as recited inclaim 4 wherein said fluid outlet has a respective hose interfaceattached thereto.
 6. An electrical machine as recited in claim 1 furthercomprising a first flange coupled to said first end and said second endof said first cooling tube.
 7. An electrical machine as recited in claim6 further comprising a second flange coupled to said first end andsecond end of said second cooling tube.
 8. An electrical machine asrecited in claim 7 further comprising a seal coupled between said firstflange and said second flange.
 9. An electrical machine as recited inclaim 8 further comprising a seal channel in said first flange, saidseal is located within said seal channel.
 10. An electrical machinecomprising: a rotor mounted on a shaft for rotation therewith anddefining an axis of rotation; a stator disposed coaxially with and inopposition to said rotor, said stator having stator windings, saidstator windings having an axially-extending portion; a first housingportion and a second housing portion enclosing said stator and saidrotor therebetween; said first housing portion having a first axial end,said first axial end having a wall with an inner surface and an outersurface; said second housing having a second axial end, said secondaxial end having a second wall with an inner surface and an outersurface; a first cooling tube having a first end and a second end and anembedded portion thereof embedded between said inner surface and saidouter surface of said first wall; a second cooling tube having a firstend and a second end and an embedded portion thereof embedded betweensaid inner surface and said outer surface of said second wall; an inletfluidically coupled to said first end of said first tube and said firstend of said second tube; an outlet fluidically coupled to said secondend of said first tube and said second end of said second tube; so thatsaid first cooling tube and said second cooling tube are fluidicallycoupled together to permit fluid flow in parallel between said firstcooling tube in said first housing portion and said second cooling tubein said second housing portion.
 11. An electrical machine as recited inclaim 10 further comprising a first flange coupled to said first end andsaid second end of said first cooling tube.
 12. An electrical machine asrecited in claim 11 wherein a second flange coupled to said first endand second end of second end of said second cooling tube.
 13. Anelectrical machine as recited in claim 12 further comprising a sealcoupled between said first flange and said second flange.
 14. Anelectrical machine as recited in claim 13 wherein said seal is locatedwithin a seal channel in the first flange.
 15. An electrical machine asrecited in claim 10 wherein said inlet and said outlet are coupled onsaid first housing portion.
 16. An electrical machine as recited inclaim 10 wherein said first end and said second end of said firstcooling tube have a common wall therebetween.
 17. An electrical machineas recited in claim 10 wherein said inlet is formed in an inlet T-shapedportion.
 18. An electrical machine as recited in claim 10 wherein saidoutlet is formed in an outlet T-shaped portion.
 19. An electricalmachine comprising: an electrical machine; a first housing portion and asecond housing portion substantially enclosing the electrical machine,said first housing portion having a first axial end; said second housinghaving a second axial end; a first cooling tube having a first end and asecond end and an embedded portion thereof embedded within said firstaxial end; a second cooling tube having a first end and a second end andan embedded portion thereof embedded between within said second axialend; a fluid interface couple to said first housing, said fluidinterface comprising, an inlet fluidically coupled to said first end ofsaid first tube and said first end of said second tube; an outletfluidically coupled to said second end of said first tube and saidsecond end of said second tube; so that said first cooling tube and saidsecond cooling tube are fluidically coupled together to permit fluidflow in parallel between said first cooling tube and said second coolingtube.
 20. An electrical machine as recited in claim 19 furthercomprising a first flange coupled to said first end and said second endof said first cooling tube.
 21. An electrical machine as recited inclaim 20 further comprising a second flange coupled to said first endand second end of said second cooling tube.
 22. An electrical machine asrecited in claim 21 further comprising a seal coupled between said firstflange and said second flange.